The present invention relates to a device to virtually represent bones or a bone joint and to a method for planning a surgical operation by using virtual representation of bones or a bone joint.
One of the most popular knee anterior cruciate ligament reconstruction procedure is the patellar tendon bone autograft. The success of the reconstruction may depend on both the selection of the intra-articular graft position and the initial graft tension. If the insertion sites, initial tension, geometry and mechanical properties of the normal anterior cruciate ligament can be restored during reconstructive surgery, the long-term complications of an anterior cruciate ligament injury can be greatly reduced.
To determine the optimal placement of an anterior cruciate ligament graft, the concept ofxe2x80x9cisometryxe2x80x9d has been advocated by many authors. A perfect isometry implies that there is no change in the distance between the ligament attachment points at the femur and at the tibia, and anisometric implies the opposite. An anisometry is said to exist when there is a change in the distance during knee flexion and extension. With an weak anisometry, the graft is subjected to nearly constant tensile forces. Accordingly, the risk of rupture because of excessive tensile force in extension or flexion is reduced and the knee stability is improved. Therefore, by positioning the central part of the ligament graft at the least anisometric sites, the possibility of excessive tensile is reduced.
A conventional method for computer-assisted knee anterior cruciate ligament reconstruction is shown in DESSENNE et al., xe2x80x9cComputer-Assisted Knee Anterior Cruciate Ligament Reconstruction: First Clinical Tests,xe2x80x9d Journal of Image Guided Surgery 1:59-64 (1995). This procedure assists the surgeon in positioning the central part of the ligament graft at the least anisometric sites.
In particular, the conventional system includes a workstation and a three-dimensional optical localizer to create images that represent knee kinematics. This surgical procedure can be performed in a typical open surgery or under use of an arthroscope. In the above described version of the system, the surgeon first drills the tibia tunnel without using the computer system. The system is then used to optimize the placement of the femoral tunnel only. The method is divided into four steps:
1) A passive flexion-extension is applied to the knee by the surgeon and for about 20-50 knee positions ranging from maximal extension to maximal flexion. At each position the location of two coordinate systems represented by optical bodies that are fixed to the femur and the tibia are computed and stored.
2) A third optical pointer is used by the surgeon to interactively collect surface points arthroscopically. Once the tibia tunnel has been developed, the center of its intra-articular extremity is digitized with the pointer. Then the surgeon acquires surface points on the femoral notch. In an area that corresponds to all possible candidate points for the femoral attachment site a set of 20-100 points is digitized.
3) Anisometry maps are then computed. The result is an xe2x80x9canisometry mapxe2x80x9d on the femoral surface that can be presented to the surgeon as a pseudo-color image. 4) This step concludes the interactive placement of the femoral tunnel. The surgeon can now locate the least anisometric point on the femoral surface using any standard surgical tool equipped with optical bodies, i.e., a drill.
Another method of determinating anisometric points at the femur and the tibia is disclosed in the EP-A 0 603 089 CINQUIN. This method uses reference bodies attached to the bones which comprise markers that can be detected by means of an opto-electronic position finder device. Furthermore, the device comprises a pointer having markers as well so that the position of the pointer tip may be computed. For a selected point at the tibia a set of points at the femur is digitized by mean of the pointer and then that point out of the set of points is computed. This shows the most invariability in distance to the selected point at the tibia during flexion and extension of the knee joint.
The present invention provides information needed to plan an anterior cruciate ligament reconstruction. In particular, it displays a surface section of a femur and/or a tibia of a knee. It may also display a ligament and planned drill holes for a knee reconstruction procedure. The extension of the ligament in case of knee flexion and extension may be digitized for any femoral or tibial attachment points and the drill holes may be planned such that they may be used as a drill guidance during the surgical operation.
More specifically, the present invention includes a system for planning a surgical operation by using virtual representation of bones and/or a bone joint. The system includes at least two reference frames each of which having first and second ends. The first end of each reference frame is configured to be affixed to the bones. The system also includes a plurality of and preferably at least three first electromagnetic or acoustic wave emitting devices attached to the second end of each of the reference frames. In addition, the system includes a moveable pointer having first and second ends, wherein the first end is a pointing tip configured to be positioned at a plurality of desired locations of the bones or the bone joint. Also, a plurality of and preferably at least three second electromagnetic or acoustic wave emitting devices are attached to the second end of the moveable pointer. Furthermore, the system includes a three-dimensional localizer device. This device includes at least two sensors and a digitizing device configured to determine three-dimensional coordinates of the first ends of the reference frames and the pointing tip based on positions and orientations of the first and second electromagnetic or acoustic wave emitting devices that are attached to the reference frames and the moveable pointer. The system also includes an image processing unit configured to generate a virtual three-dimensional surface image based on the three-dimensional coordinates of the first ends of the reference frames and the pointing tip. The virtual three-dimensional surface image includes the plurality of desired locations of the bones or the bone joint that were pointed by the pointing tip.
The computation of the location of the reference frames and the pointing tip is preferably based on the video-grammetric analysis of the images received by at least two cameras that detect the electromagnetic waves from the emitting devices. In addition, the digitizing may be based on the computation and analysis of electromagnetic wave interference patterns detected by at least three sensors that can be three linear charge-coupled device (CCD) cameras. The image processing unit enables the generation of relevant elements such as a section of the femur or the tibia, the ligament or the femoral or tibial tunnels at or between determined points on the display. Furthermore, the image processing unit permits to display any desired and previously acquired relevant element or combination of these elements from any desired angle of observation, to display stationary or moving relevant elements and allows the representation of the ligament at the display during knee flexion and extension while the resulting extension is digitized.